Spherical plain bearings typically comprise an inner member or ball positioned for rotational movement in an outer member or outer ring. The outer ring defines an inner surface contoured to receive and retain the ball therein. In one type of spherical plain bearing, an integral ball is permanently held in place by forming metal around it by, for example, swaging or coining. Alternatively, a linkage apparatus such as a rod end may have an integral ball installed therein by swaging or coining. In another type of spherical bearing, the outer ring may be constructed with a slot to permit insertion of the ball and such bearings are commonly referred to as “load slot bearings.” Alternatively, a linkage apparatus such as a rod end may have an integral ball installed therein via an entry slot machined into a face of the rod end.
Bearings in which there is metal-on-metal contact are generally used in environments in which marked variations in pressure, temperature, and high frequency vibrations are experienced. However, such variations in pressure, temperature, and high frequency vibrations can result in the bearing exhibiting high levels of wear. Moreover, high-cycle metal-on-metal contact or engagement within a short range-of-motion exacerbates the high levels of wear. Also, in these environments, foreign objects can impinge on the bearings, and contaminants such as dust, dirt, water, and aerospace fluids can be encountered, all of which can contribute to bearing wear. Additionally, high temperatures and pressures can cause severe oxidation or other forms of corrosion on the metal surfaces. This may cause a condition known as galling, leading to abrasive wear and an erosion of material.
To overcome such wear, Stellite materials and cobalt materials are typically used for manufacture of the inner member. However, neither Stellite materials nor cobalt materials have a high enough capacity for elongation to prevent the inner member from cracking under stress. A bearing with both the wear resistance of Stellite materials and cobalt materials and a high enough capacity to prevent the ball from cracking under stress has long been sought in the art. By analyzing round beams in bending, for example pins and bolts as examined by Roark and Young, a certain amount of bending stress and strain is forced into the inner member or a ball 14 of the bearing 10. FIG. 24 provides an exemplary beam deflection analysis. Alloys lacking elongation (or toughness or ductility) will crack or fracture readily, such as the brittle Stellite 3 or Stellite 6 materials having only 1% elongation. If the inner member or ball 14 is not integral with the housing 112 of the head portion 114 of the rod end 104, bushings or spacers are used. These additional components increase cost and require additional inventory to be purchased and maintained. These components further pose a foreign object damage risk during assembly of the linkage apparatus 100, the clevis joint 30, or the clevis joint within exhaust nozzle of a gas turbine engine.
A linkage apparatus or a rod end typically includes a link body shall that terminates in a head portion that defines a housing for a bearing, such as a spherical bearing. The housing is typically defined by a cylindrical interior surface. A spherical bearing installed therein typically includes a one-piece outer member or ring swaged, coined or otherwise formed around the inner member or ball. The inner member typically includes a linking shaft axially extending therethrough or integral therewith. The outer ring of the spherical bearing often has a cylindrical exterior surface complementary to the cylindrical interior surface of the housing. Rod ends can be secured to a clevis joint via the linking shaft positioned through the bearing and press fit into bores in the clevis joint. A face or corner of the rod end of the linkage apparatus may contact the inner wall of the clevis. This may also cause galling resulting in a loss of mass and weakening the structure. The linkage apparatus may also cycle back and forth, building up kinetic energy, excited by driven vibrations, leading to impact damage when the face corner strikes the clevis.
As depicted in FIG. 1A, a typical or prior art linkage apparatus 1100 includes a link body 1110 having a first rod end 1114 extending from one end thereof a second rod end 1114′ extending from an opposing end thereof. The first rod end 1114 is secured to a double shear clevis joint having two flanges 1120A and 1120A′ via a linking shaft 1130 positioned through a bearing 1140 and press fit into bores 1122 in the clevis joint flanges 1120A and 1120A′. The second rod end 1114′ is secured to a single shear clevis having one flange 1120B via a linking shaft 1130′ positioned through a bearing 1140′ and press fit into bore 1122′ in the clevis joint flange 1120B. The bearing 1140 is positioned within a cavity 1112 of a rod end 1114 and the bearing 1140′ is positioned within a cavity 1112′ of the rod end 1114′. As further depicted in FIG. 1C, the bearing 1140 includes an inner member 1142 (e.g., a truncated ball having a spherical surface) having a bore 1141 extending therethrough and positioned within an outer member 1144. An internal surface 1143 is defined by the bore 1141. As clearance develops between the internal surface 1143 and the inner member 1144 of the bearing 1140, or vector loading causes a neutation of a link body 1110A in the direction of the arrow Q1 (see FIG. 1B) and a tilting around the inner member 1142. In this type of movement, the link body 1110 is said to misalign.
As further depicted in FIGS. 1C, 1D and 1E the link body has a longitudinal axis A1. The prior art rod ends 1114 and 1114′ have two flat opposing parallel axial faces 1116 (i.e., axial with respect to axis A6) formed (e.g., milled) thereon. Each of the axial faces 1116 is spaced apart from and aligned with respective inner surfaces 1120X and 1120X′ of the flanges 1120A and 1170A′, respectively, as shown in FIG. 1E. As shown in FIG. 1F, when the rod end 1114 and link body 1110 are rotated about the longitudinal axis, for example in the direction of the arrow R1, the rod end becomes misaligned by an angle δ1. The misalignment causes each of the axial faces 1116′ (shown in dotted lines) to accelerate and impact the respective inner surface 1120X and 1120X′ of the respective flange 1120A and 1120B of the double shear clevis. Such contact causes galling 1150 as shown in FIGS. 1C and 1F.
As illustrated in FIGS. 1G and 1H, attempts have been made to employ narrow anti-rotation lugs 1118A and/or 1118B formed on one or both axial faces 1116 of the rod end 1114. The anti-rotation lug 1118A exhibits a flat top configuration and the anti-rotation lug 1118B exhibits a sharp radius profile. In addition, the anti-rotation lugs 1118A and 1118B have a relatively narrow width W1 that is less than a width W2 of an end of the bearing 1140 and less than a width W3 extending longitudinally across the flat surface 1116. However, the prior art anti-rotation lugs 1118A and 1118 B are milled and consequently exhibit troublesome tooling lines and geometries that create stress risers leading to premature fatigue failures.